1. Field of the Invention
The present invention relates to an organic semiconductor device comprising a thin film transistor (TFT) using an organic semiconductor film and a process of manufacturing the same. In this specification, the organic semiconductor device denotes the device capable of functioning by utilizing the characteristics of organic semiconductor materials on the whole, that is, it refers to active matrix type semiconductor device with a TFT provided on the same substrate. Specifically, device using a luminescent element having a film containing an organic compound (hereinafter referred to as the xe2x80x9corganic compound layerxe2x80x9d) between a pair of electrodes, capable of obtaining the fluorescence or phosphorescence by applying an electric field thereto (hereinafter referred to as the xe2x80x9cluminescent devicexe2x80x9d), electro-optical device such as a liquid crystal display device, electric appliances with the electro-optical device mounted as a part thereof, are also included in the range.
2. Description of the Related Art
In various kinds of semiconductor device storing a semiconductor element, such as a television image receiving device, a personal computer and a portable phone, a display for displaying characters and images is indispensable as a means for recognizing the information by a user. In particular, recently, a flat plate type display (flat panel display) represented by a liquid crystal display device, utilizing the electro-optical characteristics of the liquid crystal has been used actively.
As a form of a flat panel display, an active matrix driving method of displaying an image by providing a TFT per each pixel and successively writing a data signal, is known. The TFT serves as a prerequisite element for realizing the active matrix driving method.
Although such a TFT has been produced so far mostly utilizing an inorganic semiconductor material such as an amorphous silicon and a crystalline silicon, since the processing temperature in the manufacturing process for a semiconductor layer, or the like exceeds 350xc2x0 C. in the case of forming the TFT using the material, a problem is involved in that a lot of useful substrate substances cannot be used in other cases.
In contrast, a method of producing the TFT with an organic semiconductor material has been proposed. In this specification, an organic compound showing the semiconductor-like electric property of about a 10xe2x88x922 to 1016 xcexa9cm specific resistance is referred to as the organic semiconductor material, and a film formed with the organic semiconductor material is referred to as the organic semiconductor film. Moreover, the TFT produced using the organic semiconductor material is referred to as the organic TFT.
Since the organic TFT can be formed by the deposition method, the spin coating method, or the like of the organic semiconductor material, film formation can be enabled at a low temperature. Among the organic semiconductor materials, according to a soluble organic semiconductor material synthesized so as to be soluble in an organic solvent, coating methods such as the casting method and the spin coating method of forming a film by developing the solution on the substrate and drying can be utilized, and thus simplification of the manufacturing process can be expected. Furthermore, it is excellent in that the semiconductor film can be formed immediately without the need of the post treatment other than the drying operation.
However, in the case of forming a plurality of organic TFTs formed by a soluble organic semiconductor material, the patterning operation is difficult, and the method therefore is limited.
Accordingly, an object of the present invention is to provide a further sophisticated active matrix type organic semiconductor device by providing a method for forming a finer structure compared with the printing method and the ink-jet method, which have ever been used as a method for patterning a liquid material in the case of forming an organic TFT using such a soluble organic semiconductor material. Furthermore, another object is to provide an electric appliance having the organic semiconductor device.
In order to solve the above-mentioned problems, the configuration of the present invention comprises a first electrode formed in contact with an insulated surface, a first insulated film formed in contact with the first electrode, a second insulated film formed in contact with the first insulated film, having an opening part on the first electrode, an organic semiconductor film formed in the opening part in contact with the first insulated film and the second insulated film, and a second electrode and a third electrode formed in contact with the organic semiconductor film but without contact with each other.
The organic semiconductor film formed in the opening part is formed on the opening part and the second insulated film and afterwards, the organic semiconductor film formed on the second insulated film in the part other than the opening part is eliminated, and thus it has the same surface as that of the second insulated film.
Moreover, since the organic semiconductor film is formed in the opening part provided by completely eliminating the second insulated film disposed on the first electrode for functioning as the gate electrode, it is formed in contact with the first insulated film as well as it has a structure to be formed at a position superimposed with the first electrode via the first insulated film.
Here, by forming the rim of the opening part with a 45 to 60 degree taper angle, film formation of the organic semiconductor material can be facilitated.
Furthermore, the second electrode and the third electrode function each as the source electrode and the drain electrode in the organic TFT, they are formed with the same material without contact with each other. As to the material of the source electrode and the drain electrode in the present invention, since most of the semiconductor materials are a p type semiconductor for transporting the positive hole as the carrier, it is preferable to use a metal with a large work function for obtaining the ohmic contact with the semiconductor layer.
Specifically, metals capable of forming an electrode using the existing photolithography, such as gold, platinum, chromium, palladium, aluminum, indium, molybdenum and nickel, alloys using these metals, or the like are preferable.
Moreover, as the organic semiconductor material used in the present invention, a xcfx80 electron conjugate system polymer material having the skeleton of a conjugate double bond is preferable. Specifically, soluble polymer materials such as a polythiophene, a poly(3-alkyl thiophene) and a polythiophene derivative can be used.
Additionally, as the organic semiconductor material usable in the present invention, materials capable of forming an organic semiconductor film by treating after film formation of a soluble precursor can be presented. As such an organic semiconductor material obtainable via such a precursor, a polythienylene vinylene, a poly(2,5-thienylene vinylene), a polyacetylene, a polyacetylene derivative, a polyallylene vinylene, or the like can be presented.
In the present invention, these soluble organic semiconductor materials and the precursors are totally referred to as the soluble organic semiconductor materials. However, in the present invention, not only the above-mentioned materials, but also known organic semiconductor materials can be used as well.
At the time of converting the precursor to the organic semiconductor, not only the heating treatment but also addition of a reaction catalyst such as a hydrogen chloride is executed. In the case such a treatment is needed, a problem of corrosion of an electrode, or the like is involved, however, according to the structure of the organic TFT described in the present invention, there is no concern of the problem.
Moreover, as the representative solvents for dissolving these soluble organic semiconductor materials, a toluene, a xylene, a chlorobenzene, a dichlorobenzene, an anisole, a chloroform, a dichloromethane, a xcex3 butyl lactone, a butyl cellsolve, a cyclohexane, an NMP (N-methyl-2-pyrolidone), a cyclohexanone, a 2-butanone, a dioxane, a dimethyl formamide (DMF), a THF (tetrahydro furan), or the like, can be presented.
Furthermore, a process of manufacturing of the present invention for realizing such a configuration, comprises the steps of forming a first electrode on an insulated surface, forming a first insulated film on the first electrode, forming a second insulated film on the first insulated film, forming an opening part at a position with the second insulated film superimposed on the first electrode via the first insulated film, forming an organic semiconductor film on the opening part and the second insulated film, polishing the organic semiconductor film until the second insulated film is exposed, and forming a second electrode and a third electrode without contact with each other by patterning the conductive film after formation of a conductive film on the organic semiconductor film.
According to the above-mentioned process of manufacturing, an organic TFT of the present invention can be produced.
In the case of forming an organic semiconductor film using a soluble organic semiconductor material in the present invention, it is preferable to use the spin coating method.
Moreover, as a method of eliminating the organic semiconductor film formed in the part other than the opening part in the present invention, the polishing method such as the mechanical method, the chemical method and the CMP (chemical mechanical polishing) method can be presented. Furthermore, in the present invention, the ashing method can be used as well.
In the case the CMP method is used in the present invention, as a polishing agent (slurry), those including the abrasive grains such as an alumina (Al2O3), a silica (SiO2 powder) and a cerium oxide (CeO2) can be used. Moreover, as a solution for dispersing these abrasive grains, acidic or alkaline solutions such as a sulfuric acid, a nitric acid and an ammonium solution may be used, however, pure water can be used as well. Moreover, a surfactant can be used as needed. In the CMP process of the present invention, the organic semiconductor film is polished until the surface of the second insulated film is exposed.